I. Field of the Invention
The present invention relates to a wavelength converter for use in wavelength division multiplexed optical communications systems. More particularly, the present invention is directed to an interferometer wavelength converter having an integrated continuous wave probe source and/or integrated optical pre-amplifier(s).
II. Description of the Related Art
Wavelength division multiplex (WDM) networks benefit from the flexibility of wavelength converters due to the reduction in network blocking probability that such converters provide and because wavelength conversion at selected nodes in the network enables decentralized wavelength allocation management. One of the most-practical all-optical wavelength conversion schemes is cross-phase modulation in an interferometric configuration containing semiconductor optical amplifiers (SOA). Essentially, such a configuration consists of a three-port interferometer device, such as a Michelson or Mach-Zehnder interferometer, wherein an input optical signal is provided to a first port, a continuous wave beam from a light source such as a laser is provided to a second port, and an output signal is generated from a third port. The wavelength of the input optical signal is converted to the wavelength of the light source and is delivered, as so converted, from the third port of the device. The benefits of such a wavelength conversion scheme include conversion efficiency, extinction ratio enhancement and low chirp characteristics. However, it suffers from coupling losses resulting from coupling the continuous wave input to the interferometer, and from polarization variations of the continuous wave input. Furthermore, its input signal dynamic range, i.e., the range of input signal powers that is acceptable, is fairly small, typically 3 or 4 dB.
A goal of the present invention is to ameliorate the disadvantages, while retaining the benefits of an interferometric design. This is accomplished by monolithic integration, i.e. fabrication on the same chip of an interferometer, a continuous wave laser, and a pre-amplifier for the input signal. By the very nature of monolithic integration, such a fabrication removes the need for a fiber connection between the continuous wave laser and the interferometer, and therefore diminishes coupling losses between these components. The preamplifier not only provides gain, but also allows controlled gain for adjusting the input signal power available to the power required by the interferometer.